At the beggining of X-Men: The Last Stand, Charles Xavier had the ability to walk, but at the end of X-Men: First Class Charles got shot in the back and lost the ability to walk. They must have missed that when they where making First Class. Also, not only was Charles walking in Last Stand, but Magneto was there, which meens they were still friends, but that's imposible because also at the end of First Class, Magneto turns evil. Charles is also walking in X-Men Origins: Wolverine when he takes all of the prisoners of of Three Mile Island. I'm sure other people have found it out, too.
[[Video:X-Men Origins - Profesor X scene|thumb|300px|left|Charles' scene in X-Men Origins: Wolverine]]